1. Field of the Invention
This invention relates to securing stator windings and more particularly to supporting exciter winding bars in the slots of the stator core of a dynamoelectric generator incorporating an excitation potential source that is integral within the generator.
2. Description of the Prior Art
Y. S. Haggett, in "Large Steam Turbine-Driven Generators", published by General Electric Company, Schenectady, N.Y., December, 1978, provides a comprehensive description of dynamoelectric machines used in the production of electrical power. For proper operation of the turbine-generator, certain auxiliary equipment is required, and one of the major items is an excitation system which functions to provide magnetizing power to the rotating generator field winding.
The reference points out that the basic requirements of the excitation system are to furnish direct current to the field winding at a relatively low voltage (300-500 volts) compared to the generator stator voltage. One source of power which has proved to be practical in providing a high reliability excitation sytem is a commutator-type dc generator, usually driven from the generator shaft by mechanical drive. A second source is an ac alternator and rectifier combination which includes an ac alternator mechanically driven from the generator shaft, the output from which is low-voltage ac fed through rectifiers to provide dc to the generator field. Another type employs a transformer source of ac power used in conjuction with rectifiers to provide dc, wherein the source may be from the main generator leads through a special transformer.
New designs for static excitation systems have been developed to displace the time-proven shaft-driven rotating exciters. The GENERREX excitation system is a static excitation system, and an innovative design developed by General Electric Company, is integral within the generator itself, and is described by G. W. Cotzas et al, "Description and Tests of the GENERREX Excitation System for Large Steam-Turbine Generators", IEEE Trans., Vol. PAS-95, No. 3, May/June 1976, pp. 803-810. The GENERREX-CPS (Compound Power Source) excitation system utilizes both generator voltage and current, and was developed to meet the demand for both high initial response and high response ratio performance characteristics. Thus, excitation system response ratios of 3.5 have been supplied.
Historically, the majority of excitation systems have been supplied with a response ratio of about 0.5 per unit. Although a definite trend is observed in recent years toward higher performance levels, significant interest remains for the base level of 0.5 response. The GENERREX-PPS (Potential Power Source) excitation system, incorporating a potential power source integral to the generator, has been developed to meet this demand. It has been described in a paper by G. M. Cotzas et al, "GENERREX-PPS (Potential Power Source) Excitation System for Wisconsin Power & Light, Edgewater 5", presented at the Forty-Third Annual American Power Conference, Chicago, Ill., Apr. 27-29, 1981. The concept of the GENERREX-PPS excitation system retains many desirable features of the GENERREX-CPS system. Accordingly, compact arrangement of equipment is provided for reduced space requirements and simplified maintainability of the generator. Control of generator field voltage is by means of direct high-speed thyristor action. The excitation potential source consists of a winding made up of three excitation potential conductors or potential bars (each hereinafter referred to as a "P" bar) heretofore mounted on the stator in the stator-rotor air gap.
In the GENERREX-PPS system the slot support for the "P" bar is also desirable to provide uninterrupted and unyielding radial and transverse support, along the entire length of the stator core for the life of the dynamoelectric generator, against running forces which act continuously at twice the power frequency; and against sudden short-circuit forces which would occur rarely, if at all, but which are much more severe than the normal running forces. In addition, the insulated "P" bar must be allowed to move axially with respect to the support system as its temperature and that of its surroundings vary. The support must be designed so that continuous operation and repeated thermal cycling will not result in failure of the supporting structures or the insulation which isolates the "P" bar from the electrical ground.
It is, therefore, an object of the present invention to provide a new, improved support system for securing the "P" bars of the excitation system of a dynamoelectric machine in the slots of the stator core in such a manner as to be able to withstand the normal operating conditions of the dynamoelectric machine and those transient conditions which might occur as a result of misoperation.